1. Field of the Disclosure
The present disclosure relates to an amorphous high-k thin film for a capacitor of a highly integrated memory device and a manufacturing method thereof, and more particularly, to an amorphous high-k thin film using Bi—Ti—Al—O (BTAO) based materials with an amorphous microstructure as a capacitor of a memory device, and a manufacturing method thereof.
2. Description of the Related Art
According to Moore's law, the integration of a dynamic random access memory (DRAM) increases about 4 times every 3 years and the design rule continuously decreases. Accordingly, a plane space occupied by a unit cell continuously decreases. In the case of a DRAM cell consisting of one transistor and one capacitor, a plane space for a capacitor inevitably decreases and thus a plane size of the capacitor decreases. Therefore, a capacitance (C) of the capacitor decreases as given by
  C  =      ɛ    ⁢          A      t      
where, ε is a dielectric constant,
A is an effective area, and
t is a thickness of a dielectric thin film.
Even though the feature size of a device continuously reduces, a capacitance (>25 fF/cell) for the operation of the DRAM must be maintained. Therefore, many attempts have been made to reduce a thickness of a dielectric thin film and increase the area. Recently, many studies for replacing a traditional dielectric thin film (i.e., SiO2) with a high-k oxide film have been made.
In the semiconductor industries, a high-k thin film is used in a gate oxide film and a dielectric film of a DRAM capacitor. The recent research for the gate oxide film focus on Hf— or Zr-based oxide films and oxide films formed of group-III metals such as lanthanide. The high-k gate oxide film has a large leakage current because of its narrow band gap, and the thermal stability deteriorates at a high temperature when the gate oxide film contacts with a silicon surface. Recently, many research efforts have been directed to attempting to solve these problems of the dielectric thin film by adding SiO2 or Al2O3, which has good thermal stability and a large band gap (refer to Journal of Applied Physics, 87, 484 (2000); Appl. Phys. Lett. 80, 3385 (2002); Appl. Phys. Lett.81, 1071 (2002)).
However, the thin film formed by mixing the high-k material and SiO2 or Al2O3 has an amorphous microstructure and its dielectric constant becomes remarkably small. For this reason, the use of the amorphous mixed phase as the dielectric material of the capacitor has not attracted attention. For example, in the crystalline thin film with the Perovskite structure, when (Ba,Sr)TiO3 thin film (BST) having a dielectric constant of 250 or more becomes amorphous, its dielectric constant is reduced to about 25.
The capacitor dielectric of a Gbit DRAM must have a physical thickness of below about 15 nm and a thickness of an oxide equivalent film must be below about 1 nm. Therefore, it is impossible to use the amorphous dielectric thin film. Accordingly, crystalline high-k thin films have been investigated. However, if the crystalline high-k thin film becomes thin up to about 15 nm, a leakage current increases through the grain boundary.
Meanwhile, when high-k material formed of multi components such as BST is applied to a capacitor, it is very difficult to deposit a thin film having a uniform composition in three-dimensional patterns in the capacitor with the three-dimensional structure. Since the charge-to-radius ratio of group-II metals, such as Ba or Sr is small, the precursor structure is unstable and vapor pressure is insufficient.